Method and apparatus for producing window glass sheets



July 4, 1967 ZELLERS, JR ET AL 3,329,491

METHOD AND APPARATUS FOR PRODUCING WINDOW GLASS SHEETS Original FiledOct. 4, 1957 4 Sheets-Sheet l IN VEN TORS a deaf/1., (w g? wmc, c. 066aJwapz A TTORNE YS BY 2W f/m 22 .5 2@

July 4, 1967 .1. T. ZELLERS. JR, ET AL 3,329,491

METHOD AND APPARATUS FOR PRODUCING WINDOW GLASS SHEETS Original FiledOct. 4, 1957 4 Shets-Sheet 2 INVENTORS eloaL, a,

By Ale/3;

ATTORNEYS y 4, 1967 J. T. ZELLERS. JR, ET AL 3,329,491

METHOD AND APPARATUS FOR PRODUCING WINDOW GLASS SMEETS Original FiledOct. 4, 195'? 4 Sheets-Sheet 5 IN VEN TORS fizz/ma BY padr/ZZZZ.

A TTORNEYS July 4, 1967 J. T. ZELLERS, JR, ET Al. 3,329,491

METHOD AND APPARATUS FOR PRODUCING WINDOW GLASS SHEETS Original FiledOct. 4. 1957 4 Sheets-Sheet 7 IN V EN TORS am .I. dlmd, 9a., BY

A TTORNE YS and polished surfaces.

3,329,491 METHOD AND APPARATUS FOR PRODUCING WINDOW GLASS SHEETS JamesT. Zellers, Jn, Charleston, W. Va., Roy A. Ny-

quist, Toledo, Ohio, and Henry R. Meriwether, Jr., Shreveport, La.,assignors to Libbey-Owens-Ford Glass Company, Toledo, Ohio, acorporation of Ohio Continuation of application Ser. No. 95,455, Mar.13, 1961, which is a continuation of application Ser. No. 688,305, Oct.4, 1957. This application Sept. 2, 1964, Ser. No. 395,355

7 Claims. (CI. 6584) This application is a continuation of our copendingapplication Ser. No. 95,455, filed Mar. '13, 1961, now abandoned, whichin turn is a continuation of our earlier application Ser. No. 688,305,filed Oct. 4, 1957 (now abandoned.

The present invention relates broadly to the production of so-calledsheet or window glass, and more particularly to improved techniques andapparatus for producing such glass with a minimum of distortion.

The term window or sheet glass, as used herein, is intended to mean flatdrawn glass having fire polished surfaces attained during the sheetformation, as distinguished from plate glass which has mechanicallyground As is well known, commercial sheet or window glass is produced bydrawing a sheet or ribbon from a mass of molten glass directly intofinal usable form, and requires no subsequent surfacing treatment toimpart smoothness and transparency. However, one of the disadvantages offlat drawn sheet glass has been waviness or so-called distortion in thefinished product. Such distortion is due to a lack of thicknessuniformity or, differently expressed, to alternately thick and thinareas in the glass sheet. Different varieties of distortion are known inthe art by various names which have been coined to designate specifictypes. Among these are long wave distortion, short wave distortion,hammer, batter, etc.

It is our belief that these distortion defects in sheet glass are due tothe presence of non-uniform and uncontrolled conditions within thewindow glass furnaces. More specifically, we believe they are due to :alack of sufficiently uniform temperature conditions from side to side ofthe stream or channel of molten glass flowing toward and into the zoneof sheet formation, and also to the adverse influence of thermallyinduced air or convection currents that move toward, along and aroundthe newly formed sheet.

Moreover, We have actually proven that the distortion difiiculties thathave heretofore been considered to be almost a characteristic of, aswell as a necessary evil in commercial window glass production can beovercome by proper control of atmospheric and temperature conditionswithin the furnace.

Therefore it is the primary aim of this invention to substantiallyreduce, if not to entirely eliminate distortion defects in window glass,and distortion problems in its production.

Another object of the invention is to accomplish the above purpose byspecial control of air movements within the sheet glass furnace.

Another object is to assist in accomplishing the desired results bycorrectly regulating the temperatures in the molten glass across thewidth of the furnace.

Another object is the provision of special procedures and combinationsof apparatus for carrying out the above aims.

Still another object is to generally improve temperature uniformity inwindow glass furnaces and to so eliminate alternate hot and coldstreaks, lines, spots and the like in the molten glass.

* United States Patent Other objects and advantages of the inventionwill become more apparent during the course of the followingdescription, when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate likeparts throughout the same:

FIG. 1 is a fragmentary plan view of a window or sheet glass furnace andparticularly of the refining and working end thereof;

FIG. 2 is a transverse vertical sectional view through the coolingchamber of the furnace of FIG. 1, taken substantially along the line 22;

FIG. 3 is a fragmentary transverse, vertical sectional view through thedrawing chamber of FIG. 1, as taken on line 3-3;

FIG. 4 is a longitudinal sectional view taken substantially along theline 4-4 of FIG. 1;

FIG. 5 is a longitudinal sectional view of an extension of the drawingchamber shown in FIG. 4, and of the forward end of the annealing lehrconnected thereto;

FIG. 6 is a horizontal sectional plan view taken on line 6-6 of FIG. 4;

FIG. 7 is an enlarged detail view of the special width maintaining rollsof the invention;

FIG. 8 is a fragmentary sectional view at the end of the coolingchamber, showing a modified form of structure; and

FIGS. 9, 10 and 11 are longitudinal sectional views through the coolingchambers and draw-pots of three modified forms of the invention.

Referring now more particularly to the drawings, and with specificreference to FIG. 1, there has been illustrated therein the refining andworking end of a continuous sheet glass furnace which is designated inits entirety by the numeral 18. Conventional furnaces of this charactergenerally include a gas fired regenerative type melting tank 19 whichsupplies molten glass to one or more suitable refining or conditioningchambers. As here shown, there are provided a pair of such refiningchambers, separated by a crotch Wall 20, and one of which has beenillustrated at 21. Although in no way restricted thereto, the presentinvention is particularly well adapted for use with a so-called Colburntype of sheet glass drawing machine and it will be described in thatconnection here. Thus, the forward end of the refining chamber 21 isjoined by a cooling chamber 22 to a draw-pot 23 positioned below adrawing or forming chamber 24 (FIGS 1 and 4).

Now with a continuous tank furnace such as just described, a mass ofglass 25 is melted in the melting tank 19 and flows from the melting endinto and through the refining chamber 21 within which it is properlyconditioned. From the refining chamber the molten mass moves through thecooling chamber 22 where it is gradually brought down toward workingtemperature, and finally it flows into the working receptacle ordraw-pot 23 from which a sheet or ribbon of glass may be continuouslydrawn.

The draw-pot 23 in a conventional Colburn type window glass machine issupported upon stools 27 within a pot chamber 28 which is heated by gasflames from burners 29 introduced into and through the walls 30.

A sheet or ribbon of glass 31 is continuously drawn upwardly from thesurface of the molten bath within the draw-pot and, while still in asemi-plastic condition, although substantially set in its final sheetform, is deflected into the horizontal plane about a bending roll 32 andthen passed over a so-called idler or intermediate roll 33 and through aflattening chamber 34 wherein the said ribbon is supported and carriedforwardly upon a series of horizontally aligned machine rolls 35. Theribbon advances from the drawing and flattening chamber 34 into a lehr36 wherein it is supported and carried along upon a series ofhorizontally aligned rolls 37 until suitably annealed.

Now it has been customary in most attempts to improve window glassdistortion to take the corrective measures only in and around the zoneof sheet formation. We agree that this is of considerable importance.But we have also found that for the very best results certain steps canand preferably should be taken long before this.

To illustrate, it has heretofore been considered to be impossible toproduce window glass without ream unless skim bars were employed in therefining chamber and, in

- fact, it has been conventional to provide so-called skim pockets 38 inthe side walls 39 of the furnace for use therewith. Such skim bars servea useful purpose but they do have bad features and, in addition, thereis approximately a twenty minute loss in production every time they haveto be cleaned.

Now we have found that when we introduce cooling air through the skimpockets 38 by means of pipes 40 we can remove the skim bars and stilleliminate ream in this area. Moreover the cooling air also acts tostabilize the glass temperature in advance of the cooling chamber toeven-out hot and cold streams and improves both yield and metal quality.

The importance of ream elimination in any anti-distortion program is ofcourse obvious because the presence of the different kinds of glasswhich show up as ream produce and are responsible for cordiness in thefinished glass sheet.

Another important feature of the invention which has a directrelationship to the introduction of cooling air into the refiningchamber is the locating of a special cutoff bar 41 partially above andpartially below the molten glass at the entrance to the cooling chamber22. This bar which is here shown as of generally L-shape may have anenlarged portion 42 on the upper end of the vertical leg and apreferably angled ledge 43 on the upper surface of the horizontal legand acts to provide both an air and a liquid seal between the coolingand refining chambers.

This seal makes it possible to introduce sufficiently large amounts ofcooling air through the pipes 40 into the refining chamber to accomplishthe purposes already set forth, and also to nullify the adverse effectsof the pressure change in the refining chamber that results from theflame reversal at the regenerators. We have determined that thispressure change has heretofore been largely responsible for theproduction of streaks of cross ream as a result of alternately followingcold and hot streams of air and combustion gases from side to side ofthe furnace.

Another advantage of being able to introduce the larger amounts ofcooling air into the refining chamber is that it permits removal ofcertain pipe coolers that were formerly used close to the glass in thevicinity of the zone of sheet formations to maintain drawing speed butwhich concededly produced hammer in the finished sheet.

Because of its special shape, the bar 41 also sets up a backflow of hotglass toward the side edges of the cooling and refining chambers nearthe glass surface that assists in establishing more uniform glasstemperature conditions across the cooling chamber. Thus, this shape ofbar produces a downward and then upward flow of molten glass as itenters the cooling chamber 22 which results in a continual surge ofglass onto and laterally along the lip 43 of the bar. As the lateralflow lessens, the glass again flows downwardly and in so doing causes areturn flow of the cooled glass in the edge areas and in the vicinity ofthe side walls of the chambers with the result that such glass becomessubject to a rearward current which operates to return the cooled glassinto the refining chamber 21 and toward the higher temperature moltenglass in the melting zone of the furnace.

Although generally referred to as a cooling chamber the chamber 22 maybe more aptly described as a heat extracting chamber since thetemperature of the glass passing therethrough is usually lowered throughradiation of heat therefrom to at least as great an extent as bypositive cooling. Consequently, improved temperature uniformity can beachieved by insulating the longitudinal margins of the cap 47 and theside walls 48 as shown at 47 and 48 respectively. In this way radiationfrom the normally cooler side areas of the glass stream will be retardedand, of course, the insulation can be of graduated thickness and extentto give a controlled retardation of heat radiation. Furtherstabilization of temperature may be achieved within the chamber 22 bythe introduc tion of cooling air into this chamber also through pipes44, 45 and 46.

As best seen in FIG. 2, the pipe 44 is vertically disposed in thechamber arch or cap 47 while oppositely disposed pipes 45 are mounted tointroduce air through the chambers side walls 48. Pipe 46' extendsacross the chamber adjacent the glass surface and is provided with anaxially aligned slot 49 formed in the lower surface thereof andpositioned to direct an air stream downwardly onto the glass.

By introducing air into the cooling chamber in this way a somewhatpressurized control can be exerted to counteract the entry of outsideair. In other words, the pressure of air introduced through pipes 44, 45and 46 can be proportioned to create a static condition along the walls48 of the chamber; and pipes 45 and 44, being of a common pressure, willstabilize the ambient air within the chamber and across the glasssurface. This will tend to equalize the surface temperature and the airemanating from the slot 49 in pipe 46 can be controlled to uniformlyreduce and to assist in equalizing the surface temperature of the moltenglass flow-ing therebeneath.

The importance of this regulated introduction of volumes of air ino thecooling chamber and the more or less pressurized control of theatmosphere in this chamber can best be appreciated when it is understoodthat such outside influences as barometric pressures, that vary hour byhour, normally act to set up unbalanced pressure conditions between theoutside atmosphere and that in the furnace. This has heretofore resultedat least periodically, in an objectionable influx of dirt-carrying airfrom the outside through the furnace wall structures to create anundesirable turbulence in the furnace atmosphere. Moreover, because theaction resulting from the unbalanced pressure condition varies in degreethroughout the arch area of the chamber, it produces downwardly flowingstreams of air which alter the thermal characteristics of the glasssurface in a non-uniform manner to develop streaks of relatively coolglass even in areas of normally high temperatures.

The introduction of cooling air into the refining and cooling chambersin the several ways that has just been described, and the special mannerin which this air is controlled and applied, is part of the overall aimof this invention to equalize the temperature of the moving stream ofmolten glass across its entire width and to thereby create asubstantially uniform consistency in the stream of molten glass in everystrata thereof at any given cross-sectional area.

One more item which contributes to this purpose, and which also acts toput what might be termed a cooled layer on the surface of the glasswhereby to help maintain the speed of draw, is a plurality ofsuperimposed cooler pipes 50 near the discharge end and closely adjacentthe end wall 51 of the cooling chamber. These pipes, as best seen inFIGS. 2 and 4, are formed with a downwardly urving middle section 52which approaches quite closely to the surface of the molten glass andside sections 53 which are positioned a slightly greater distance abovethe molten stream. They are preferably water-cooled and act to extractheat from and so reduce the temperature of the central, and relativelyhotter, area of the molten stream to a greater extent than thetemperature of the relatively cooler side areas.

As a further means of bringing the temperature of the edge glass up tothat at mid-stream, electrodes 55 may be arranged in the side areas ofmolten glass under and at either side of the wall 51 and spacedsufficiently to pass electrical energy through the molten glass flowingtherebetween to heat the same by the Joule effect. The electrodes 55 arepreferably located slightly below the glass surface and can be increasedin number along the walls of the cooling chamber as desired. In fact,additional electrodes, as indicated at 56, may be employed in moresubmerged positions to carry out the heating effect and to more rapidlybring the edge glass to the desired temperature.

The last and perhaps the most important control feature in connectionwith the cooling chamber is the provision of an angled or sloped bottom57 therefore and which as here shown preferably extends over the majorportion of the length of the cooling chamber. In order to morecompletely understand the operation of this angled bottom arrangement itshould be understood that one of the characteristics of the Colburn typeof sheet glass drawing machine is the relatively shallow draw-pot orworking receptacle from which the ribbon of glass is drawn. One of theprincipal functions of the so-called cooling hamber in connection withsuch a machine, in addition to its primary function of bringing glasstemperature down to working level, is to provide a channel through whichthe molten glass flows from a relatively deep refining chamber to therelatively shallow draw-pot.

Heretofore the change of level has been accomplished by the use of oneabrupt step at the exit end of the refining chamber and a secondsomewhat more gradual but still quite steep step, usually in the form ofa so-called goose-neck, between the floor of the cooling chamber and thefloor of the draw-pot.

However, we have found that surprisingly better results from allstandpoints and including those relating to distortion problems havebeen obtained by the substitution of a long, sloped bottom in thecooling chamber for the prior stepped construction. The primary actionof this sloped arrangement is that it permits a smooth uniform flow ofglass from the refining chamber into and through the cooling chamber andinto the draw-pot that effectively eliminates any serious formation ofdevitrified glass or dog metal in and around the cooling chamber.

As indicated above, the important feature seems to be that the change inlevel between the bottom wall of the refining chamber and the bottomwall of the pot be a gradual and a continuous one with no sharp changesin level or interruption to glass flow as the depth of the channeldecreases from that of the refining chamber to that of the draw-pot. Theactual length of the sloped bottom of the cooling chamber seems to be ofless importance since excellent results have been obtained when thesloped bottom 57 of the cooling chamber extended from a similarly slopedbottom 58 of the refining chamber that lead to the full refining chamberdepth as shown in FIG. 9; and good results have also been obtained whenthe sloped cooling chamber bottom 57 terminated at the entrance end ofthe cooling chamber as shown in FIG. 10; and also when it terminatedsomewhat inwardly of the entrance end of the cooling chamber in a flatbottomed portion of the same depth as the refining chamber as shown inFIG. 11.

In any event there is a definite relationship between the slope of thecooling chamber and the location of the bar 41. Thus, it appears thatthe bar 41 must be so located relative to the sloped bottom 57 as toprovide a sufficient depth of glass therebeneath. Our work stronglyindicates that there must be at least twelve inches of glass between thebottom of the bar 41 and the bottom of the cooling chamber directlytherebeneath for completely satisfactory operation.

It will also be seen from the above that the sloped bottom of thecooling chamber and the side electrodes in the exit end of the coolingchamber have somewhat similar and overlapping functions. In other words,each of these different features acts to eliminate dog metal and toreduce edge drag. This is extremely important in the matter ofeliminating distortion because it makes possible a uniform flow of glassthrough the shallowing channel between the refining chamber and thedraw-pot and consequently assists in maintaining a uniform temperatureacross the width of the molten glass moving through the restrictedchannel.

The accumulative effect of the various controls that have been thus fardescribed is to bring the stream of molten glass to the draw-pot 23properly conditioned, free of defects, and at a uniform temperature of adegree compatible with the thickness and speed at which the glass sheetor ribbon 31 is being drawn.

We again want to emphasize the extreme importance, in eliminatingdistortion defects in the finished glass ribbon, of the describedcontrol treatment and channeling of the glass stream. Admittedly theprocedures from this point on, and especially in the actual zone ofsheet formation and in the area where the glass is drawn from the molteninto the solid state, are also extremely important and, in someinstances at least, may properly be said to be even more critical thanthe preforrning procedures.

However, we have discovered that the very best results in eliminatingdistortion defects in the commercial manufacture of window glass areobtained when the proper combination of pre-drawing, drawing andpost-drawing techniques are employed.

Probably one of the most important procedures in the actual drawing orforming of the glass ribbon, insofar as it relates to the prevention ofdistortion defects in the sheet being produced, is the feature ofmaintaining the forming chamber 24 within which the sheet is drawn asnearly as possible a closed chamber. In this Way it is possible tomaintain a substantially quiescent atmosphere in and around the newlyformed sheet and to properly control any air movements that may be setup in the area.

As best shown in FIGS. 3, 4 and 6, the forming chamber 24 and theadjoining flattening chamber 34 are normally defined and partiallyenclosed by an end wall 51, which also serves as the end wall of thechamber 22, by oppositely disposed side walls 59 and by a roof 60. Thebottom of the flattening chamber 34 is closed by the wall 61, while thebottom of the forming chamber 24 is substantially closed off from thedraw-pot by conventional front and back lip-tiles 62 and 63 respectivelywhich also act to define, between their opposed faces 64 and 65, theactual zone of sheet formation 66 within the drawing chamber 24.

Observation bays or openings 67 are provided in the side walls 59, andthese openings can also be used to connect certain of the operatingmechanism of the drawing machine to its drive means outside of thedrawing chamber. However, these openings are conventionally providedwith transparent closures (not shown) which embody portions that fitclosely around any parts projecting therethrough and effectively sealthe drawing chamber against any substantial movement or infiltration ofair into or out of the chamber at these points.

In the operation of the so-called Colburn type machines, provision mustbe made to prevent devitrification of the glass in the relativelystagnant rear or closed end of the draw-pot. It has heretofore beencustomary to shape the inside of the rear wall of the pot chamber 28 andthe bottom surface of the rear lip-tile 63 in a manner designed todirect the hot gases and products of combustion from the pot chamberupwardly, laterally and then downwardly over the rear wall 68 of thedraw-pot onto the molten glass adjacent thereto.

However, we have found that this prior method of increasing thetemperature of the glass in the rear end of the draw-pot is a serioussource of dirt, uncontrolled air currents and other defect producingconditions. And, in accordance with the present invention, We propose tocompletely close off the pot chamber from the area above the moltenglass, and to provide :a different route for the removal of the productsof combustion from the pot chamber.

As best indicated in FIG. 4 this can be accomplished by the provision ofan inverted T shaped partition or wall 69, extending between the uppersurface of the rear wall of the draw-pot and the bottom surface of thelip-title 63, in combination with passageways 70, in the bottom wall 61,that are connected to a suitable duct 71 (FIG. 5) leading to aconventional exhaust fan system or stack (not shown). A thermocouple 71can be arranged in the passageways 70 to control the temperature of thegases passing therethrough by regulating the exhaust means. This way ofexhausting the products of combustion from the pot chamber also servesthe additional purpose of counteracting the normal tendencyof the hotupwardly rising pot gases to infiltrate into the drawing chamber as aresult of the normal stack action within the chamber.

The vertical wall 72 of the partition 69 is preferably made as thin asis practicable without too greatly reducing its structural strength inorder to permit it to transmit as much radiant heat as possible into thespace beneath the liptile 63 and onto the surface of the molten glass inthe draw-pot. Even so, however, the partitioning off of the glass in thepot from the pot chamber may result in the glass at the rear of thedraw-pot being too cool.

To overcome this possibility, and to further equalize the temperature ofthe molten glass in the drawpot from side to side thereof, electrodes 73are provided. These electrodes are preferably positioned in the area ofthe rear corners of the draw-pot, and may either be inserted through theside walls of the pot or, as shown in FIG. 4, may be supported so as toextend downwardly into the molten glass. When power is applied, therewill be a tendency for the electrical energy to go from the electrode atone corner of the pot to the electrode at the other corner of the potand to so heat the glass along the back of the pot by Joule effect.However, experience has shown that, with electrodes positioned in themanner indicated in the drawings, the greater part of the current willflow from the electrodes through the side edge portions of the glass inthe pot through the metal Width maintaining devices 74 and 75, acrossthe meniscus of the rising sheet to the corresponding Width maintainingdevices on the opposite side and thence through the glass in the sideedge of the pot to the other electrode.

This direction of current flow is of material assistance in obtainingthe proper temperature of the molten glass in and around the meniscus,in preventing undue chilling of the glass by the width maintainingmeans, and in otherwise promoting uniformity of temperature throughoutthe molten glass that is actually going into the rising sheet.

To this same end the lip-tiles 62 and 63 may be insulated as shown at 62and 63' to assist in equalizing the temperature from side to side of theglass stream beneath the lip-tile 62 and to retard radiant heat lossfrom the glass beneath the lip-tile 63 in the stagnant end of thedraw-pot.

In addition to its function of closing off a portion of the lower partof the forming chamber 24 from the draw-pot, the upper portion of thelip-tile 63 also acts to partially partition off that part of theflattening chamber 34 which lies beneath the horizontal run of the glassheet 31 from the portion of the forming chamber 24 immediately adjacentthe zone of sheet formation 66. To complete the partitioning in thisarea there is provided a bar 76 mounted on top of the lip-tile andhaving a curved upper surface 77 which substantially conforms to thecurve of the idler roller 33.

As shown in FIG. 5, the lower part of the flattening chamber 34 ispartitioned ofl from the lehr 36 by a brick wall 78 and the upper partby a curtain 79 of a flexible material such as glass fibers that issuspended for vertical adjustment by cables 80 from a rotatably mountedshaft 81. A second adjustable curtain 79' can be used with or withoutthe curtain 79 to cut oif the flattening area and lehr from the drawingarea above the horizontal run of the glass ribbon.

To provide for any necessary air or gas removal from the forming chamber24 and flattening chamber 34, there is provided a stack or flue 82 (FIG.5) equipped with an adjustable damper plate 83 for closely regulatingthe exhaust therefrom. By proper control of the damper plate 83,uncontrolled air movements can be prevented and a very minimum of stackaction through the drawing and flattening chambers can be establishedand maintained. Besides taking care of any necessary removal of gas orair from the chambers 24 and 34, the stack 82 also provides a means forby-passing and removing air that might otherwise filter into thedischarge end of the flattening chamber either from the outside or fromthe lehr 36.

A similar action in by-passing and removing incoming air that mightinfilter through the machine enclosure due to pressure changes in theoutside atmosphere is eflfected by exhaust pipes 84 positioned atopposite sides of the drawing chamber in the zone of sheet formation(FIG. 4). We have found such an arrangement to be of considerableimportance since it is virtually impossible to provide a completely airtight enclosure for glass making furnaces or machinery.

Air may be exhausted from the drawing chamber 24 by various means andfrom many positions, but thus far we have had the best results whenusing a pair of independently controlled exhaust pipes at Opposite sidesof the chamber and positioned one on each side of the sheet very near tothe surface of the molten glass.

Of course the by-passing of air as described above is only one of thefunctions of the exhaust pipes 84. An even more important one is that ofmaintaining a static or slightly sub-atmospheric pressure within thedrawing chamber and particularly in the zone of sheet formation. This isof great value in maintaining a quiescent atmosphere around the newlyformed sheet and in preventing unwanted and uncontrolled air movementsand convection current being set up. In the same Way, the pull of thepipes 84 can be so regulated, with relation to the action of the stack82, as to completely obviate any stack action within the actual zone ofsheet formation and to maintain a relatively quiescent atmosphere forthe ribbon of glass from the point of its formation tothe lehr.

Before leaving the matter of machine enclosures, and the control of theair movements within such enclosures, it is important to point out thatit has been customary in the operation of so-called Colburn type drawingmachines to play gas flames on or in the vicinity of the newly-formedsheet for the purpose of controlling the temperature or plasticity ofthe glass; and that we have discovered that the presence of such gasflames within the machine enclosures has been a considerable factor inthe creation of undesirable air movements within the enclosures.

Nevertheless adequate means for localized heating of the glass ribbonare important, and we have found that this can be provided without theobjectionable features of gas burners by substituting suitableelectrical heating means for the burners wherever it is desired toselectively heat the glass ribbon within the enclosures.

Thus, electrical resistance heaters 85 may be provided on opposite sidesof the rising sheet adjacent the margins thereof for heating the sheetedges just before they reach the bending roll. Similar heaters 86 may beprovided to act on the sheet edges while the glass is actually beingbent from the vertical into the horizontal plane, and still other units87 of the same character may be employed to control the temperature ofthe sheet edges as they move into the flattening chamber.

It will be appreciated that there are many details of the conventionalColburn type sheet drawing machines that have not been illustrated inthe drawings of this application, and other details that have beenillustrated but not described since they are neither original with theapplicants here nor necessary to the practice of the invention. In thislatter category are such items as the sheet coolers 88 and the bendingroll cooler 89, all of which are conventionally employed in one form oranother in producing window and sheet glass by the Colburn method.

This same thing may be said of the width maintaining devices previouslyreferred to, insofar as the present inventions being dependent on theuse of any specific form of width mantaining devices is concerned. As amatter of fact, a large number of various types of width maintainingdevices have been tried and used even commercially on Colburn typemachines. In all cases they engage the edges of the rising glass sheetat the meniscus and act to overcome the inherent tendency of a drawnglass sheet to narrow to a thread. Perhaps the most widely used and bestknown form of width maintaining devices are the so-called knurled rolls,and we prefer to use with maintaining devices of this general type inpracticing our invention.

However, we have found that the use of a new and particular form ofroller type width maintainer, in combination with the other features ofour invention, may actually have some part in overcoming certaindistortion defects that would otherwise be present in the finishedsheet. This is because these different width maintaining rolls have beenfound to eliminate the cup or wave adjacent the sheet edges that hasbeen a characteristic of the conventional knurled rolls, as well asacting to widen the sheet which is their primary purpose.

This special roller width maintaining device, which is best shown inFIG. 7, comprises a pair of knurled rolls 74 similar to the conventionalknurl rolls and a pair of smaller smooth rolls 75 positioned near thebase of the sheet 31. The pairs of rolls 74 or 75 may be water or aircooled but we have operated them successfully with no cooling at all.The auxiliary or lower pair of rolls 75 are spaced apart 'sufiicientlyto reduce the thickness of the meniscus, indicated at A, to a lesserthickness, as is indicated by the letter B. Both the smooth rolls 75 andknurl rolls 74 are positively driven, preferably at the same r.p.m.However, the peripheral speeds will be different, and a definite draw isimposed on the sheet edge C by reason of the rolls 75 being of a smallerdiameter than the upper knurl rolls 74. This causes the rolls 74 to drawor stretch the glass between the pairs of rolls and to thin down theedge C. In actual practice, this produces a sheet of glass having agreater width of acceptably useable glass, and greatly reduces the cupor wave defect.

A modified form of closure for the discharge end of the cooling chamber22 has been illustrated in FIG. 8. This consists primarily in thesubstitution of a generally L-shaped block 90 for the pipe cooler 50 asshown in FIG. 4. The block 90 is very similar to the block 41 at theentrance end of the cooling chamber except that it is somewhat smaller,has a rounded lower rear surface 91 to facilitate movement of the moltenglass therebeneath, and is provided with an opening 92 to receive asupport bar 93. The block 90 functions in the same manner as the block41 to provide an air and liquid seal or cut-off for the discharge end ofthe cooling chamber, and to carry the relatively hot glass at the middleof the stream toward and rearwardly among the margins by lateral andback flow of surface glass along the ledge 94.

To insure sufficient space between the bottom wall of the block 90 andthe inclined floor of the cooling cham- 10 her (it should not be lessthan six inches) it may be necessary, in addition to reducing the sizeof the block, to provide different angles of slope 95 and 96 in thecooling chamber floor and which meet just below the block as at 97.

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as a preferred embodiment of the same, but thatvarious changes in the shape, size and arrangement of parts may beresorted to without departing from the spirit of the invention or thescope of the subjoined claims.

We claim:

1. In a method of producing Window glass in sheet form and substantiallyfree of distortion from a continuous window glass furnace that containsa mass of molten glass and in which the atmosphere above the glass inthe furnace is confined, by first melting the glass in a relatively deeparea at one end of said furnace, flowing it therefrom through successiverefining and cooling areas into a relatively shallow working area at theopposite end and drawing it upwardly therefrom in sheet form; the stepsof maintaining at least part of the confined atmosphere above the glassin the cooling area separate from and independent of the confinedatmosphere upstream thereof, causing the upper strata of molten glassfrom said refining chamber to move downwardly toward, upwardly into andlaterally within said cooling area and gradually, uniformly andcontinuously reducing the depth of the molten glass in said furnace fromthe depth at the relatively deep melting end to the depth at therelatively shallow working end substantially within said cooling area.

2. In a continuous window glass furnace comprising a relatively deepmelting tank, a relatively deep refining tank, a cooling tank and arelatively shallow working receptacle arranged in end to endcommunicating relationship with side walls and a roof confining theatmosphere above the molten glass in said furnace, a Wall hermeticallysealing off at least part of the confined atmosphere above the moltenglass in said cooling tank from the confined atmosphere above t-hemolten glass upstream thereof and under which the upper strata of moltenglass from said refining tank must pass into the cooling tank, a slottedpipe extending transversely of said cooling tank within the confinedatmosphere thereabove for introducing cooling air into said confinedatmosphere and directing it toward the surface of said molten glass, anda bottom wall in said cooling tank at least a portion of which is slopeduniformly and continuously upward from the level of the bottom wall ofsaid relatively deep melting tank to the level of the bottom wall ofsaid relatively shallow working receptacle.

3. In a continuous window glass furnace comprising a relatively deepmelting tank, a relatively deep refining tank, a cooling tank and arelatively shallow working receptacle arranged in end to endcommunicating relationship with side walls and a roof confining theatmosphere above the molten glass in said furnace, a wall hermeticallysealing off at least part of the confined atmosphere above the moltenglass in said cooling tank from the confined atmosphere above the moltenglass upstream thereof and under which the upper strata of molten glassfrom said refining tank must pass into the cooling tank, and a bottomwall in said cooling tank at least a portion of which is slopeduniformly and continuously upward from the level of the bottom wall ofsaid relatively deep melting tank to the level of the bottom wall ofsaid relatively shallow working receptacle.

4. In a method of producing window glass in sheet form and substantiallyfree of distortion from a continuous window glass furnace that containsa mass of molten glass and in which the atmosphere above the glass inthe furnace is confined, by first melting the glass in a relatively deeparea at one end of said furnace, flowing it therefrom through successiverefining and cooling areas into a relatively shallow working area at theopposite end and drawing it upwardly therefrom in sheet form; the stepsof maintaining at least part of the confined atmosphere above the glassin the cooling area separate from and independent of the confinedatmosphere upstream thereof, gradually, uniformly and continuouslyreducing the depth of molten glass in said furnace from the depth at thedeep melting end thereof to the depth at the shallow working end thereofsubstantially within said cooling area, directing the upper strata ofmolten glass from said refining area first downwardly and then upwardlyinto said cooling area, and introducing cooling air into each of saidseparated and independent confined atmospheres above the glass.

5. In a method of producing window glass in sheet form and substantiallyfree of distortion from acontinuous window glass furnace that contains amass of molten glass and in which the atmosphere above the glass in thefurnace is confined, by first melting the glass in a relatively deeparea at one end of said furnace, flowing it therefrom through successiverefining and cooling areas into a relatively shallow working area at theopposite end and drawing it upwardly therefrom in sheet form; the stepsof gradually, uniformly and continuously reducing the depth of moltenglass in said furnace from the depth at the deep melting end thereof tothe depth at the shallow working end thereof substantially within saidcooling area, and directing a stream of air extending at an angle to thedirection of flow of molten glass through said furnace onto the surfaceof the molten glass in said cooling area.

6. In a method of producing window glass in sheet form and substantiallyfree of distortion from a continuous window glass furnace that containsa mass of molten glass and in which the atmosphere above the glass inthe furnace is confined, by first melting the glass in a relatively deeparea at one end of said furnace, flowing it therefrom through successiverefining and cooling areas into a relatively shallow working area at theopposite end and drawing it upwardly therefrom in sheet form; the stepsof maintaining at least part of the confined atmosphere above the glassin the cooling a-rea separate from and independent of the confinedatmosphere upstream thereof, gradually, uniformly and continuouslyreducing the depth of molten glass in said furnace from the depth at therelatively deep melting end thereof to the depth at the relativelyshallow working end thereof substantially within said cooling area,directing the upper strata of molten glass from said refining area firstdownwardly and then upwardly into said cooling area, and introducingcooling air into the separated and independent confined atmosphere abovethe glass in the cooling area by directing a stream of air extending atan angle to the direction of flow of molten glass through said furnaceonto the surface of the molten glass in said cooling area.

7. In a continuous window glass furnace comprising a relatively deepmelting tank, a relatively deep refining tank, a cooling tank and arelatively shallow working receptacle arranged in end to endcommunicating relationship and each having a bottom wall, at least aportion of the bottom wall of said cooling tank sloping uniformly andcontinuously upward from the level of the bottom wall of the relativelydeep melting tank at one end of said furnace to the level of the bottomwall of the shallow working receptacle at the opposite end thereof, saidfurnace having side walls and a roof confining the atmosphere above themolten glass in said furnace, a wall hermetically sealing off at leastpart of the confined atmosphere above the molten glass in said coolingtank from the confined atmosphere above the molten glass upstreamthereon and under which the upper strata of molten glass from saidrefining tank must pass into the cooling tank, and means for introducingair into the confined atmosphere above the molten glass in the coolingtank and for introducing cooling air into the independent and separateconfined atmosphere upstream thereof.

References Cited UNITED STATES PATENTS 1,547,797 7/1925 Ewing -261,606,409 11/1926 Fowle 65-202 1,676,027 7/1928 Harvey 65-83 1,726,1148/1929 Morton 65-157 1,888,496 11/1932 Ferngren 65-355 1,953,023- 3/1934Mul'holland 65-135 1,980,992 11/1934 Ha'lbach 65-345 2,049,600 8/1936Wright 65-137 2,064,546 12/ 1936 Kutchka 65-206 2,121,958 6/1938 Formanet al. 65-95 2,478,090 8/1949 Devol 65-137 2,726,486 12/1955 Brichard65-8 2,911,759 11/1959 Pilkington 65-157 2,945,325 7/1960 Deible et al.65-178 DONALL H. SYLVESTER, Primary Examiner.

D. CRUPAIN, F. W. MIGA, Assistant Examiners.

5. IN A METHOD OF PRODUCING WINDOW GLASS IN SHEET FORM AND SUBSTANTIALLY FREE OF DISTORTION FROM A CONTINUOUS WINDOW GLASS FURANCE THAT CONTAINS A MASS OF MOLTEN GLASS AND IN WHICH THE ATMOSPHERE ABOVE THE GLASS IN THE FURNACE IS CONFINED, BY FIRST MELTING THE GLASS IN A RELATIVELY DEEP AREA AT ONE END OF SAID FURNACE, FLOWING IT THEREFROM THROUGH SUCCESSIVE REFINING AND COOLING AREAS INTO A RELATIVELY SHALLOW WORKING AREA AT THE OPPOSITE END AND DRAWING IT UPWARDLY THEREFROM IN SHEET FORM; THE STEPS OF GRADUALLY, UNIFORMLY AND CONTINUOUSLY REDUCING THE DEPTH OF MOLTEN GLASS IN SAID FURNACE FROM THE DEPTH AT THE DEEP MELTING END THEREOF TO THE DEPTH AT THE SHALLOW WORKING END THEREOF SUBSTANTIALLY WITHIN SAID COOLING AREA, AND DIRECTING A STREAM OF AIR EXTENDING AT AN ANGLE TO THE DIRECTION OF FLOW OF MOLTEN GLASS THROUGH SAID FURNACE ONTO THE SURFACE OF THE MOLTEN GLASS IN SAID COOLING AREA.
 7. IN A CONTINUOUS WINDOW GLASS FURNACE COMPRISING A RELATIVELY DEEP MELTING TANK, A RELATIVELY DEEP REFINING TANK, A COOLING TANK AND A RELATIVELY SHALLOW WORKING RECEPTACLE ARRANGED IN END TO END COMMUNICATING RELATIONSHIP AND EACH HAVING A BOTTOM WALL, AT LEAST A PORTION OF THE BOTTOM WALL OF SAID COOLING TANK SLOPING UNIFORMLY AND CONTINUOUSLY UPWARD FROM THE LEVEL OF THE BOTTOM WALL OF THE RELATIVELY DEEP MELTING TANK AT ONE END OF SAID FURNACE TO THE LEVEL OF THE BOTTOM WALL OF THE SHALLOW WORKING RECEPTACLE AT THE OPPOSITE END THEREOF, SAID FURNACE HAVING SIDE WALLS AND A ROOF CONFINING THE ATMOSPHERE ABOVE THE MOLTEN GLASS IN SAID FURNACE, A WALL HERMETICALLY SEALING OFF AT LEAST PART OF THE CONFINED ATOMOSPHERE ABOVE THE MOLTEN GLASS IN SAID COOLING TANK FROM THE CONFINED ATMOSPHERE ABOVE THE MOLTEN GLASS UPSTREAM THEREON AND UNDER WHICH THE UPPER STRATA OF MOLTEN GLASS FROM SAID REFINING TANK MUST PASS INTO THE COOLING TANK, AND MEANS FOR INTRODUCING AIR INTO THE CONFINED ATMOSPHERE ABOVE THE MOLTEN GLASS IN THE COOLING TANK AND FOR INTRODUCING COOLING AIR INTO THE INDEPENDENT AND SEPARATE CONFINED ATMOSPHERE UPSTREAM THEREOF. 